1. Field of the Invention
The embodiments of present invention relate to a detection circuit and a detection method for a liquid crystal display.
2. Discussion of the Background
In the structure of a liquid crystal display, an alignment film may control liquid crystal molecules to produce optical rotation, wherein its orientation angle and pre-tilt angle are critical conditions enabling the liquid crystal molecules to produce optical rotation. The manufacture procedure of the alignment film includes the processes of coating and rubbing alignment film, bubbles generated in coating process and broken after rubbing process and rubbing scratches caused by particles and foreign matters and so on during the rubbing process would cause the alignment film being partially damaged, as illustrated in FIG. 1. FIG. 1 is an illustrative diagram of the alignment film formed after the rubbing process, alignment film 2 is formed on a pixel area 1 of a substrate in FIG. 1. The pixel area 1 comprises 9 sub-pixels, alignment film damage 3 occurs on the alignment film of some of sub-pixels in the pixel area 1. In case of damage to the alignment film, the normal orientation angle and pre-tilt angle of the alignment film no longer exist, which causes turbulence to the liquid crystal molecules, so that the liquid crystal molecules could not produce optical rotation effect controlled by the voltage on both ends of the pixels electrode as in the normal situation, thus resulting in the light leaking phenomenon, which would cause abnormal display in the damaged area of the alignment film, and white dot occurs.
As to the detection of the white dot in the damaged area of the alignment film, it is generally achieved through the detection for the liquid crystal cell after the cell assembly process, as illustrated in FIG. 2. FIG. 2 is an illustrative diagram of the structure of a circuit for detecting cell in the prior art. Said circuit includes a timing controller 4, a source driver 5 and a gate driver 6. The timing controller 4, as a core component for a display drive, usually is user customized chip, which could output various signals to the source driver 5, such as a frame ON signal, a column clock pulse signal and a polarity inversion signal. The polarity inversion signal could act as a role of preventing liquid crystal molecules from aging and reducing crosstalk interference of the signals between the adjacent pixels in display driving. The timing controller 4 outputs the polarity inversion signal to the source driver 5, the display data signal to be displayed in the cell 7 to be detected also enters into source driver 5, which performs the digital-analogue conversion on the display data signal according to the preset reference voltage and polarity inversion signal, generates pixel voltage signal and outputs the pixel voltage signal to the cell 7 to be detected, and it would be under the control of the row scan signal output by gate driver 6 in outputting the pixel voltage signal to the cell 7 to be detected, the pixel electrode of each pixel in the cell 7 to be detected receives a pixel voltage signal generated by source driver 5 according to polarity inversion signal and display data signal. In particular, polarity inversion signal could control the polarity of the pixel voltage signal, thus the cell 7 to be detected forms different polarity inversion modes, such as two rows inversion mode and single row inversion mode, and so on. FIG. 3 is an illustrative diagram of the two rows inversion mode in the prior art, and FIG. 4 is an illustrative diagram of the single row inversion mode in the prior art. As illustrated in FIG. 3 and FIG. 4, the row inversion mode shown in FIG. 3 is two rows inversion mode, namely, the pixel voltage signal received by the cell to be detected is a signal whose polarity changes once every other two rows; the row inversion mode shown in FIG. 4 is single row inversion mode, namely, the pixel voltage signal received by the cell to be detected is a signal whose polarity changes once every other one row; meanwhile, because the polarity of each pixel shown in FIG. 4 is contrary to the polarity of the adjacent pixel thereof, in this situation, the polarity inversion mode shown in FIG. 4 can also be referred to as dot inversion mode. Reference could be made to FIG. 5 with respect to the control to the polarity of pixel voltage signal by the polarity inversion signal. FIG. 5 is an illustrative diagram of wave of the input polarity inversion signal vs. the wave of the output pixel voltage signal, wherein, the polarity inversion signal is a periodical square wave signal, which could control the polarity of pixel voltage signal, so as to form the two rows inversion mode of FIG. 3. When the input polarity inversion signal is a signal with a high level, the output is pixel voltage signal with positive polarity, i.e., pixel voltage signal having a voltage value higher than the common electrode signal; when the input polarity inversion signal is a signal with a low level, the output is pixel voltage signal with negative polarity, i.e., pixel voltage signal having a voltage value lower than the common electrode signal.
However, because the damage to the alignment film normally happens in a very small area, such as in the area of the 9 sub-pixel shown in FIG. 1, and there are glutinosity effect or crosstalk interference of the signals between liquid crystal molecules in said area and liquid crystal molecules of the surrounding normal areas, and the selectivities to the light through the upper and lower polarization sheets (the polarization directions are orthogonal), there is a problem that it is difficult to discriminate the display effects of the damaged area of the alignment film and the normal area, for example, it is difficult to discriminate the display effects of the damaged area and the normal area under the above described two rows polarity inversion mode and single row polarity inversion mode. Therefore, in the detection process, it is difficult for the operator to recognize the white dot of the damaged area of alignment film, and missing detection easily occurs.